Zero valent iron and clay mixtures for removal of trichloroethylene, chromium(VI), and nitrate

Abstract

A series of batch experiments on free swell, hydraulic conductivity, and contaminant removal efficiency was performed for the combination of bentonite and zero valent iron (ZVI), in order to identify the optimal mixing ratio between bentonite and ZVI. The swell volume of the bentonite-ZVI mixtures did not change with increasing ZVI, and the hydraulic conductivity decreased as the ZVI increased. The reduction rates and removal efficiencies of trichloroethylene (TCE), Chromium(VI), and nitrate increased as ZVI content increased, while there was no practical difference in removal efficiencies between 30% and 100% of ZVI weight contents. Therefore, 30% of the ZVI content was used as the optimal amount in this research since the physical properties, such as swell volume and hydraulic conductivity, as well as the contaminant sorption and reduction were the most efficient. From Raman spectrophotometer analysis, peaks of magnetite, maghernite, and hematite were observed on the surfaces of the bentonites that had been used for the mixtures. Since iron oxides are strong adsorbers of contaminants and magnetites can facilitate the electron transfer of irons, these formations are beneficial for the long-term performance of the iron metals.